Composite containers for packaging products under pressure, particularly, refrigerated dough products, constitute a significant commercial consumer product. Typically, the containers are formed of a helically wound paperboard or boardstock layer; an interior layer which is a laminate including kraft paper, foil and/or polymer layers; and an exterior label. The helically wound boardstock layer includes an unglued butt joint formed by the adjacent edges of the boardstock extending helically from end to end of the can. The exterior label surrounds the boardstock and covers the butt joint thereby preventing the premature opening of the butt joint.
Commercially significant containers of this type are disclosed in U.S. Pat. No. 3,981,433 to Thornhill et al. which is directed to one-step easy-open containers including an inner liner having a helical pleat positioned opposite the unbonded helical butt joint. When the outer wrapper is removed, the dough and liner expand outwardly together as the liner pleat begins to unfold. The resultant pressure on the can body causes the butt joint to open. This in turn automatically allows the inner liner to expand further. The liner is automatically opened by the rapidly expanding dough to thereby allow access to the dough in the interior of the container.
The outer label surrounding the butt joint in containers of this type is an important structural component of the container because the outer label bridges the butt joint and maintains it in the closed position. Accordingly, the label must be strong in order to prevent premature opening of the container. In addition, liquids from the product in the container, e.g. dough, can seep out of the product into the ends of the easy-open seam and be channeled down the seam. The label must also be able to withstand exposure to such liquids. These structural requirements for the label prevent the use of more economical low strength sheet materials for construction of the label.
The outer label must also be easily removable in order to expose the easy-open seam for opening of the container. Typically, the label includes a tab for grasping by the consumer, and which when pulled, initiates a tear in the outer label allowing the label to be removed in whole or in part sufficiently to expose the easy-open seam. However, if the tab is pulled carelessly by the consumer, the label can tear in the wrong direction and only a portion of the easy-open seam may be exposed. In such instances, removal of the remaining portion of the label covering the easy-open seam and the opening of the container body can be frustrating to the consumer.
When a thick kraft paper is used in the outer label to meet the structural requirements for the label, still another difficulty can be created. As the label is pulled away from the can body, the thick kraft paper can split into layers, between its outside and inside surfaces. In this case, only the outer portion of the label is removed leaving a thin paper layer covering the easy-open scam. Removal of this thin layer can be particularly difficult.
Numerous modifications have been proposed for easy-open spirally wound composite containers. For example, an easy-open container having a spirally wound lap joint is proposed in U.S. Pat. No. 3,221,975 to Zoeller et al. The overlapping edge of the joint is permanently clued to the underlying ply. A plurality of discontinuous perforations are provided in the overlapping seam so that the overlapping seam itself, forms a tear strip for opening of the container.
It has also been proposed to provide a separate reinforcing strip bonded to the container body in overlapping relation to the butt joint. Such separate tensile members are proposed in U.S. Pat. No. 3,102,818 to Zoeller; U.S. Pat. No. 3,972,468 to Reid; and in U.S. Pat. No. 3,940,496 to Turpin et al. The use of separate tensile members bridging the butt joint provides improved strength across the butt joint and can allow for the use of lighter weight outer label sheet materials. However, the addition of the separate tensile member increases the costs of the container and complicates the manufacturing process.
Despite these and numerous other proposals for modifying the known spirally wound easy-open containers, commercially available easy-open containers still typically employ a relatively thick outer label construction which adds to the costs of the container and, in addition, removal of the outer label is not always accomplished in a reliable fashion to ensure exposure of the easy-open seam of the container body.